Solar collector panel for heating ventilation air

ABSTRACT

A solar collector panel is disclosed for heating of air, in which the conventional insulation material on the back panel facing away from the sun is replaced by a spacing between a permeable back panel and a permeable heat absorber means, so that a heat convection airflow through the back panel and into the interior of the solar energy panel against the temperature gradient prevents the convection heat loss in the opposite direction. The back panel also reduces the radiation heat loss from the heat absorber means. Furthermore, in case the flow of air through the solar energy panel is stopped, the convection-insulation will no longer be effective, and a photovoltaic cell panel placed within the solar energy panel and generating electricity from the solar radiation will not be subjected to the damaging high stagnation temperature of a traditionally insulated solar collector panel.

The present invention relates to a solar collector panel for collectionof thermal energy by heating of air, in which the conventionalinsulation material on the back panel facing away from the sun isreplaced by the heat convection airflow through a permeable back paneland into the interior of the solar energy panel against the temperaturegradient.

Furthermore, in case the flow of air through the solar collector panelis stopped the convection-insulation will no longer be effective, and aphotovoltaic cell panel placed within the solar collector panel andgenerating electricity from the solar radiation will not be subjected tothe damaging high stagnation temperature of a traditionally insulatedsolar collector panel.

BACKGROUND

Solar collector panels for heating of water for domestic use or forspace heating are well known in the art, but also solar collector panelsfor heating of air, either to be used directly for ventilation and spaceheating or as a medium for conveying heat to a heat exchanger is known.

The French patent application FR 2500036 shows a typical, simple solarcollector panel comprising a transparent front panel, a heat absorbingback panel which is thermally insulated at the back wall, and a passagebetween the front panel and the back panel, which has an inlet openingat the bottom for allowing cold air to flow into the passage and anoutlet opening at the top for exit of the air heated by passing the backpanel. The back wall of the back panel facing away from the front panelis thermally insulated to prevent a heat flow from the heat absorbingback panel and out of the solar collector panel.

U.S. Pat. No. 4,054,124 discloses a more sophisticated solar collectorpanel, in which a perforated heat absorber panel is inserted between thetransparent front panel and the thermally insulated back panel. Theinlet air flows from the side of the solar collector panel into thespace between the front panel and the heat absorber panel, through theperforations at which the air is heated and out from the space betweenthe heat collector panel and the thermally insulated back panel. A muchhigher heat transfer coefficient between the air and the heat absorberis obtained thereby as compared to the disclosure of FR 2500036.

In U.S. Pat. No. 4,262,657 more variants of solar collector panels aredisclosed, using the feature of a permeable heat absorber panel throughwhich the air flows to be heated. It is a common feature of the variantsthat the back wall of the solar collector panels is thermally insulatedto improve the thermal efficiency of the solar panel.

The combination of a solar collector panel for heating of air and aphotovoltaic cell panel arranged behind the transparent front panel andin front of the heat collector panel is disclosed in GB 2 214 710. Theheat collector plate is thermally insulated towards the exterior and atransparent panel between the photovoltaic cell panel and the heatcollector panel separates airflows parallel to the panels to cool thephotovoltaic cell panel and to extract heat from the heat collectorpanel, respectively.

It is an object of the present invention to provide a solar collectorpanel with a construction that simplifies the manufacturing of the solarcollector panel and secondarily improves the reliability of the coolingof a photovoltaic cell panel arranged within the solar collector panel.

The solar collector panel according to the present invention comprises aback panel that is permeable to air and open to the surroundings over amajor part of the area covered by the front panel, an air permeable heatabsorber means extending between and spaced from the front panel andsaid back panel, and an air outlet opening extending from between thefront panel and the heat absorber means to the exterior of the solarcollector panel. Thereby, the air flows into the solar collector panelthrough the back panel against the temperature gradient and replaces thethermal insulating material as long as there is airflow. From there, theair flows through the heat absorber means and out through the outletopening to be used for ventilation and space heating for e.g. vacationcottages, yachts, cabins, storage containers, cellars, stables andcaravans. Other advantages of the present invention and the particularpreferred embodiments are disclosed in the following description.

The space between the permeable back panel and the permeable heatabsorber means serve as a thermal insulation while the solar collectorpanel is operating and thus replacing the thermal insulation materialused in the art, such as rock wool panels. The substantially uniformlydistributed airflow from the colder back panel to the warmer heatabsorber means has a direction opposite the temperature gradient andprevents a convection heat loss from the heat absorber means. Heat lossdue to radiation in the infrared spectrum from the heat absorber meansis effectively reduced by the back panel, which reflects a part of theradiation back to the heat absorber means and absorbs the remaining partas heat energy, which is returned into the solar collection panel by thecold air flowing through the permeable back panel from the surroundings.

The pressure drop of the airflow over the back panel promotes thehomogeneity of the airflow distribution over the area spanned by thesolar collector panel. This provides the advantage that the airflowvelocities are generally low in most of the solar collector panel, withthe possible exception of the area close to the outlet, even for solarcollector panels spanning a large area or more solar collector panelcoupled to each other, as opposed to the traditional solar collectorpanels having one common air inlet and a generally high velocity of theair. Low velocities means low pressure losses and low generation ofnoise, and the low air velocity at the intake of air into the solarcollector panel, i.e. at the back side of the back panel, has thefurther effect that only small dust particles are carried with the airflow into the solar collector panel as larger and more heavy particlesare less susceptible to be accelerated by the low air velocity. Thus, anair cleaning effect on the ventilation air exhausted from the solarcollector panel is obtained as well and filtering of the ventilation airmay be reduced or made redundant. The solar collector panel and inparticular the permeable parts and the possible filters will besubjected to dust to a reduced extend, thus requiring less maintenanceand cleaning of the solar collector panel.

A further advantage of the construction of a solar collector panelaccording to the invention is that it is particularly suitable forhaving a photovoltaic cell panel arranged therein, as the constructionreduces the risk of excessive heating of the photovoltaic cell panel incase the airflow through the solar collector panel is stopped. When theairflow from the back panel towards the heat absorbing means stops, thethermally insulating action of the airflow is halted as well and heatmay now flow from the heat absorber means out through the back panel bynatural convection as well as heat radiation, and the excessive heatingwith stagnation temperatures of more than 120° C. known from solarcollector panels with traditional thermal insulating material may beavoided.

BRIEF DESCRIPTION OF THE INVENTION

Thus, the present invention relates to a solar collector panelcomprising at least one transparent or translucent front panel, such asa single or double glass panel or a panel of transparent plasticsmaterial, a back panel, an air permeable heat absorber means extendingbetween and spaced from said front panel and said back panel, and an airoutlet opening extending to the exterior of the solar collector panel,which solar collector panel is novel over the known art in that the backpanel is permeable to air and open to the surroundings over a majorpart, preferably at least 75%, of the area covered by the front panel,and the air outlet opening extends from the volume enclosed by the frontpanel and the heat absorber means.

The permeability of the heat absorber means and of the back panel ispreferably substantially homogeneous and of a magnitude that allows fora convection-driven airflow through the solar collector panel due tosolar radiation on the front panel. A substantially homogeneouspermeability to air may e.g. be obtained with a sheet material with ahomogeneously distributed perforation or with woven or non-woven fabric.

The front panel, the heat absorber means and the back panel are in apreferred embodiment arranged substantially parallel. The spacingbetween the front panel and the heat absorber means is preferably in therange from 2 to 15 cm, largest when a photovoltaic cell panel isarranged in the spacing, more preferred in the range from 3 to 10 cm andthe most preferred in the range from 4 to 7 cm. The spacing between theheat absorber means and the back panel is preferably in the range from0.5 to 5 cm, and more preferred in the range from 1 to 3 cm.

It is advantageous to reduce the heat loss from the heat absorber meansdue to radiation out through the front panel. The front panel may have acoating layer on the inner side facing the heat absorber means thatenhances the reflection of radiation in the infrared range, inparticular of wavelengths in the range of 5 to 25 μm where most of theenergy of the heat is radiated from the heat absorber means, whereasmost of the energy of the solar radiation is found at lower wavelengths.

Another solution is to manufacture the front panel from a plasticsmaterial that is much less transparent to the long-wave infraredradiation from the heat absorber means than to the shorter-wave solarradiation.

Alternatively or additionally, a heat radiation trap may be applied toreduce the heat loss from the heat absorber means by infrared radiationthrough the front panel. Such traps and other means for limiting theheat loss due to re-radiation of heat through the front panel isdiscussed and disclosed in e.g. U.S. Pat. No. 4,262,657.

The heat absorber means may e.g. be a porous, dark or black fibrous mat,such as felt, or a woven or stamped screen, or a perforated platematerial. The heat absorber means may in particular be made from a platematerial with opening defined therein of a general diameter or hydraulicdiameter for the airflow through the plate, in the range from 0.7 to 3millimetres arranged with a mutual spacing in the range of 8 to 20millimetres. The material of the heat absorber means may preferably be aperforated metal plate, preferably made from aluminium but also e.g.steel plates may be employed, of a thickness in the range of 0.4 to 4millimetres, preferably of 0.7 to 3 millimetres. The side of the heatabsorber means facing the front panel is preferably dark or black andmat, so that the absorption coefficient α of the solar spectrum ofradiation, i.e. the solar absorptivity α_(s), is high, preferably in therange of 0.65 to 1, and most preferred in the range of 0.8 to 1. It isalso preferred that the side of the heat absorber means facing the backpanel has similar properties to absorb as much as possible of the heatradiation emission, mainly reflection, from the back panel.

Likewise, the back panel may be made from a plate material with openingdefined therein of a general diameter in the range from 0.7 to 3millimetres arranged with a mutual spacing in the range of 8 to 20millimetres. The permeability of the back panel should be substantiallyhomogeneous throughout its extension to promote a homogeneousdistribution of the airflow. The back panel may preferably be aperforated metal plate, preferably made from aluminium e.g. of athickness in the range of 0.4 to 4 millimetres, preferably of 0.7 to 3millimetres, but other materials may alternatively be employed as well,such as steel, various plastics materials and plywood. The side of theback plate facing the heat absorber means is preferably white or of alight colour and with a reflective surface, so that is has a reflectioncoefficient ρ of infrared radiation in the range of 0.65 to 1,preferably in the range of 0.8 to 1. The infrared radiation from theheat absorber means is in particular of wavelengths in the range of 5 to25 μm where most of the energy of the heat is radiated from the heatabsorber means, and the above reflection coefficient is mainly given forthis range of wavelengths.

The production of the solar collector panel according to the presentinvention is simplified if similar plates are used for the heat absorbermeans and the back panel, e.g. perforated aluminium plates withidentical perforation as discussed above. However, it is preferred thatthe surface properties of the two plates are different in accordancewith the particulars given previously.

Instead of using a metal plate for the heat absorber means, it ispreferred to employ a fibrous mat, in particular a screen of felt, thatshould have a dark colour or be black to absorb as much as possible ofthe solar radiation. Other types of fibrous mats may also be employed,such as woven or non-woven cloth or stamped cloth. A lower mass of theheat absorber means may be obtained by using a fibrous mat as comparedto other materials, and the insulating effect is also advantageous forpreventing heat from the spacing between the heat absorber means and thefront panel from escaping through the back panel.

In a preferred embodiment, the solar collector panel comprises one ormore photovoltaic cell panels arranged between the front panel and theheat absorber means. The one or more photovoltaic cell panels may in afurther preferred embodiment of the present invention power the drivemeans of a ventilator that is arranged to force air out through the airoutlet opening.

The present invention furthermore relates to a ventilation systemcomprising a plurality of solar collector panels according to the abovedescription, wherein the air outlet openings of said solar collectorpanels are mutually connected to a common ventilation duct with aventilator arranged to force the airflow from said solar collectorpanels out through the common ventilation duct.

BRIEF DESCRIPTION OF THE DRAWING

Embodiments of the present invention are shown in the enclosed drawingfor illustration of how the invention may be carried out, including thefollowing figures:

FIG. 1 shows a longitudinal section of a solar collector panel accordingto a first embodiment of the invention,

FIG. 2 shows a longitudinal section of a solar collector panel accordingto a second embodiment of the invention, in which a photovoltaic cellpanel and a ventilator is incorporated in the solar collector panel,

FIG. 3 shows a panel assembly comprising a plurality of solar collectorpanels according to the first embodiment, coupled together and having acommon outlet,

FIG. 4 shows a ventilation system comprising a plurality of panelassemblies of FIG. 3, where the outlets are coupled to a commonventilation duct with a ventilator arranged therein, and

FIG. 5 shows the coupling of two solar collector panels of FIG. 3 inmore details.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

A solar collector panel 1 according to a first embodiment of theinvention is shown in a longitudinal section in FIG. 1, in which analuminium frame 2 holds a transparent front panel 3 made from a 10millimetre plate of polycarbonate with elongated cavities definedtherein to lower the weight thereof and improve the thermal insulation,a heat absorber means 4 made from a screen of black felt, and a backpanel 5 made from a similar perforated aluminium sheet that is left witha blank side facing the heat absorber means 4. In an alternativeembodiment, the heat absorber means 4 is made from a perforatedaluminium sheet 0.7 millimetres of thickness, which is painted black oranodised on both sides. The solar collector panel 1 is preferablyarranged vertically as shown, and the direction of the solar radiationis indicated with arrow A. An outlet duct 6 is arranged at the upperpart of the panel 1 to form a passageway for the heated air to flow outfrom the panel 1 and to the place where it is utilised, e.g. for roomventilation and heating.

The solar radiation, arrow A, is transmitted through the front panel 3and reach the heat absorber means 4, at which more than 80% of theenergy of the solar radiation is absorbed and the remaining part isreflected out through the front panel 3. The absorbed energy causes thetemperature of the heat absorber means 4 to rise to e.g. 40°-90° C. Thiswill cause the heat absorber means 4 to radiate heat as infraredradiation, mainly in the range of 5 to 25 μm. The blank face of the backpanel 5 reflects about 70 to 75% of the radiation back to the heatabsorber means 4, whereas the remaining part is absorbed by the backpanel 5. Only a minor heat loss is caused by re-radiation of heatthrough the front panel 3 as the type of plastics used to a large extendis opaque to the long-waved radiation from the heat absorber means 4.

Air from the surroundings is, as indicated with arrows B, drawn throughthe perforated back panel 5, which is cooled so that the absorbed heatradiation from the heat absorber means 4 thereby is conveyed back intothe solar collector panel 1. The airflow passes the spacing 7 ofapproximately 2 cm width between the back panel 5 and the heat collectormeans 4 in the direction against the temperature gradient and preventsthereby effectively a convection of heat out through the back panel. Theairflow passes then, as indicated with arrows C, the heat absorber means4 where the air is heated and moves mainly upward, as indicated byarrows D, in the spacing 8 of approximately 5 cm between the heatabsorber means 4 and the front panel 3, towards the outlet duct 6arranged in the upper part, preferably near or at the top end, of thesolar collector panel 1, and out as indicated by arrow E. The heated airwill due to its buoyancy move upward in the spacing 8, and the airflowthrough the solar collector panel 1 of FIG. 1 is driven by naturalconvection.

FIG. 2 shows a longitudinal section of a solar collector panel 1according to a second embodiment of the invention, in which aphotovoltaic cell panel 9 is arranged in the spacing 8 between the frontpanel 3 and the heat absorber means 4 with a spacing 10 to the latter toallow a flow of air past the back side of the photovoltaic cell panel 9.The power output from the photovoltaic cell panel 9 is connected to themotor of a ventilator 11 with a fan that is placed in the outlet duct 6,so that a combination of buoyancy forces and the ventilator 11 drivesthe airflow in this embodiment. However, the buoyancy force is only of aminor magnitude as compared to the effect of the ventilator 11 and isnot required for the operation of solar collector panels 1 according tothe second embodiment. The ventilator 11 is sufficient to drive anairflow, and the outlet duct 6 may be arranged in any part of the solarcollector panel, not only in the upper part of the solar collector panel1 as is required for the first embodiment. The airflow indicated byarrows D cools the photovoltaic cell panel 9 and prevents excessiveheating thereof, and the amount of airflow is increased as well as thethermal efficiency of the solar collector panel 1 as compared to theembodiment of FIG. 1. In case the airflow is stopped or reduced, e.g.due to malfunction of the ventilator 11, contamination of theperforations of the back panel 5 or a blockage of the ventilation duct(not shown) extending downstream of the outlet duct 6, an excessive andpossibly destructive or duration-reducing heating of the photovoltaiccell panel 9 is prevented, as the insulating effect of the spacingbetween the back panel 5 and the heat absorber means 4 will be reducedor eliminated, and the heat loss through the back panel 5 will increasecorrespondingly.

The solar collector panels 1 according to the first embodiment as wellas to the second embodiment may in a variant for operation inenvironments that are particularly polluted with particles, comprise afilter sheet releasably mounted on the outer face of the back panel 5,so that at least some of the particles in the inlet airflow, arrows B,may be captured before they enter the interior of the solar collectorpanel 1. The releasable filter sheet may be replaced regularly, or thefilter sheet may be removed for cleaning and remounted on the solarcollector panel.

The solar collector panels I according to the two embodiments may extendover larger areas, as exemplified in FIG. 3, which shows a panelassembly 12 comprising a plurality of solar collector panels 1, 1′, 1″according to the first embodiment coupled together and having a commonoutlet duct 6. The general air velocity will be low as compared to theknown types of solar collector panels for air heating with inlet at thebottom, as the air inflow is distributed over a large area, and higherair velocities, which cause losses and noise, will only occur near theoutlet duct 6.

A ventilation system comprising a plurality of the panel assemblies 12of FIG. 3, is shown in FIG. 4 where the outlets 6 of the schematicallyshown assemblies 12 are coupled to a common ventilation duct 13 with aventilator 14 arranged therein to produce a common ventilation airflowindicated by arrow F. One or more photovoltaic cell panels 9 arranged inone or more of the solar collector panels 1 may drive the ventilator 15.

Details of the coupling of two solar collector panels 1 of FIG. 3 isshown in FIG. 5, in which an open aluminium profile 16 holds the frontpanels 3, 3′, the heat absorber means 4, 4′ and the back panels 5, 5′ ofthe two solar collector panels 1, thus allowing for a flow of heated airfrom one panel 1′ to the next 1, as indicated by the arrow G. A spacingmember 17 is provided to maintain the correct magnitude of the spacing 7between the back panel 5 and the heat absorber means 4.

1-11. (canceled)
 12. A solar collector panel for space heating andventilation, comprising at least one transparent or translucent frontpanel, a back panel, a heat absorber means extending between and spacedfrom said front panel and said back panel, one or more photovoltaic cellpanels arranged between the front panel and the heat absorber means, anair inlet opening to surroundings of the solar collector, and an airoutlet opening extending to an exterior of the solar collector panel,wherein, the air inlet opening is provided by the back panel, which ispermeable to air and open to the surroundings over a major part of anarea covered by the front panel, the heat absorber means is airpermeable, and the air outlet opening extends from a volume enclosed bythe front panel and the heat absorber means.
 13. A solar collector panelaccording to claim 12, wherein a ventilator is arranged to force air outthrough the air outlet opening, and the ventilator is driven by drivemeans powered by the one or more photovoltaic cell panels.
 14. A solarcollector panel according to claim 12, wherein the back panel is madefrom a plate material with openings defined therein of a generaldiameter in the range from approximately 0.7 to 3 millimetres arrangedwith a mutual spacing in the range of approximately 8 to 20 millimetres.15. A solar collector panel according to claim 12, wherein the backpanel is a perforated metal plate of a thickness in the range ofapproximately 0.4 to 4 millimetres.
 16. A solar collector panelaccording to claim 12, wherein the back panel at a side facing the heatabsorber means has a reflection coefficient p of infrared radiation inthe range of approximately 0.65 to
 1. 17. A solar collector panelaccording to claim 12, wherein the heat absorber means is made from aplate material with openings defined therein of a general diameter inthe range from 0.7 to 3 millimetres arranged with a mutual spacing inthe range of 8 to 20 millimetres.
 18. A solar collector panel accordingto claim 12, wherein the heat absorber means is a perforated metal plateof a thickness in the range of 0.4 to 4 millimetres.
 19. A solarcollector panel according to claim 12, wherein the heat absorber meansis a fibrous mat.
 20. A solar collector panel according to claim 12,wherein the heat absorber means at a side facing the front panel has anabsorption coefficient a of solar spectrum of radiation in the range ofapproximately 0.65 to
 1. 21. A ventilation system, comprising: aplurality of solar collector panels according to claim 12, wherein theair outlet openings of said solar collector panels are mutuallyconnected to a common ventilation duct with a ventilator arranged toforce airflow from said solar collector panels out through the commonventilation duct.
 22. Method of producing and heating a flow of air forventilation and space heating, using the solar collector panel of claim1, the method comprising: drawing air into the panel from thesurroundings through the back panel, heating the air within the panel,and leading the heated air from the air outlet opening and into thespace to be ventilated and heated.
 23. A solar collector panel accordingto claim 15, wherein the metal plate is made from aluminium.
 24. A solarcollector panel according to claim 18, wherein the metal plate is madefrom aluminium.
 25. A solar collector panel according to claim 19,wherein the fibrous mat comprises a screen of felt.